Apparatus for dispensing flowable substances, particularly adhesives, paints, varnishes, and release agents are used, for example, in order to apply adhesives to a substrate, portion by portion. In this connection, application of the adhesives takes place controlled by way of a metering valve, where application as a line, point, spray, spiral, or surface area is particularly possible.
In the processing of flowable substances with metering valves, it is problematic that residues of the substance can accumulate at the outlet of the metering valve, and, particularly if they harden there, can disrupt subsequent operation of the apparatus or can actually bring it to a complete stop.
To avoid such difficulties, an apparatus is proposed in DE 41 13 445 A1.
In this apparatus, the control element has a slide, the end of which is configured so that it can be slid over an exit opening of the nozzle and closes or opens the latter directly. The slide is an elongated metal plate that is rectangular in cross-section and is disposed in a slide housing in which there is a return spring that holds the slide in the closed position. In this connection, a closure piece situated in a recess on the closure-side end of the slide, which consists of a silicone sponge saturated in oil or anti-adhesion agent, or of a wedge-shaped plastic part inclined toward the exit opening of the nozzle forms the actual closure. The slide housing is firmly connected with a support arm, on which an accommodation holder for a metering valve that has the nozzle is also attached. Furthermore, a compressed air connector is situated on the support arm, and when this is actuated, the slide is pushed into the open position and, in this connection, the opening in the slide gets under the exit opening, thereby making it possible for the substances to be applied to the substrate. When the closure piece is moved into its closed position, a leading edge of the closure piece first makes contact with the free nozzle, before the closure piece contacts the free nozzle end over the full area with its surface facing the nozzle end and closes off the exit opening of the nozzle. This action of the free nozzle end on the leading edge during every closing procedure of the closure part leads to increased wear of the leading edge and thereby to a reduced useful lifetime of the apparatus. Aside from this, the control element used in the apparatus requires a relatively large construction space. This is particularly disadvantageous if multiple apparatuses, i.e. multiple nozzles must be disposed relatively closely next to one another, side by side, and therefore little room is available in this direction of placement of apparatuses.
An apparatus for dispensing flowable substances is furthermore described in DE 199 36 670 C1. This apparatus has a fixed support, a metering valve connected with this support, having an exit nozzle for the flowable substances, as well as an outer closure part for closing the exit opening of the nozzle. In this connection, the closure part is disposed in stationary manner and the metering valve or the nozzle is pivoted relative to the closure part. In this embodiment, as well, a leading edge of the closure part contacts the nozzle in the region of the free nozzle end during the closing procedure, in each instance, resulting in the disadvantage described, that of increased wear of the closure part in the region of the leading edge. This apparatus, too, does not have a compact construction, because of the pivoting arrangement of the metering valve.
An apparatus for dispensing flowable substances, having a nozzle and a closure part for the nozzle, is furthermore known from EP 0 719 592 A2. In this apparatus, as well, a leading edge of the closure part contacts the nozzle in the region of its free nozzle end when the closure part is moved into its closed position.